指派问题的回溯算法，回溯算法解决此问题要找出问题所有的可行解，然后一次比较保留问题的最优解(即最少耗费的解)，并输出结果-The assignment problem, backtracking algorithm retrospective algorithm to solve the problem of finding problems all feasible solution, then a comparative retain the optimum solution of the minimum cost solution (namely) and output